Stent delivery devices proposed heretofore are used to secure a lumen or a space in a body cavity by implanting the stent at the lumen, the stenosed portion or the closed portion of the body cavity in an internal organ such as the blood vessel, the bile duct, the trachea, the esophagus, the ureter, the digestive tract, and the like.
The stent is classified into a self-expandable stent and a balloon expandable stent in dependence on the function thereof and an implantation method.
The balloon expandable stent which itself has no expanding function. To implant the stent at a desired portion, after the stent is inserted into the desired portion, a balloon disposed in the stent is inflated to expand (thermoplastically deform) the stent by an expansive force of the balloon so that the stent is fixed, with the stent in close contact with the inner surface of the desired portion.
It is necessary to perform the above-described operation of expanding the stent of this type in implanting it in the desired portion. The stent can be implanted in the desired portion by directly mounting on the contracted balloon. Thus the balloon expandable stent does not have a problem in this respect. But the stent does not have an expansive force by itself. Therefore there is a possibility that the diameter of the stent becomes smaller due to the pressure of the blood vessel with an elapse of time and that a constriction occurs again.
On the other hand, the self-expandable stent itself has contracting and expanding functions. To implant the stent at a desired portion, after it is inserted into the desired portion in a contracted state, an applied stress is released to maintain the contracted state. For example, the stent is accommodated in a sheath having a smaller diameter than the inner diameter of the desired portion by contracting the stent. After the distal end of the sheath reaches the desired portion, the stent is pressed out of the sheath. Because the stent is released from the sheath, the applied stress is removed. Thereby the stent returns to the original configuration. Thereby the stent adheres to the inner surface of the desired portion.
Unlike the balloon expandable stent, it is unnecessary to perform the operation of expanding the stent of this type in implanting it in the desired portion. Further there is no possibility that the diameter of the stent becomes smaller due to the pressure of the blood vessel and that a constriction occurs again.
As compared with the balloon expandable stent, it is difficult to implant the self-expandable stent correctly at the desired portion for the reason described below. After the stent is disposed at a desired stenosed portion, a liquid is injected into a balloon. Thus the stent does not move longitudinally when the stent is expanded. The delivery system of the self-expandable stent has a construction in which the stent is restrictedly accommodated between an inner tube and an outer tube, and a locking portion for restricting the movement of the stent is provided in the inner tube at a position located at the proximal side of the stent. By pulling the outer tube toward the proximal side of a system, the stent is released from the restricted state and expands itself. The stent is liable to move forward when it expands owing to loosening of the outer tube inside a body cavity and friction between the stent and the body cavity, between the stent and a catheter or between the stent and a valve of a device called an introducer for introducing the delivery system into a patient's body.
In the system constructed of three tubular members described in WO96/31174, the outermost tube is provided in addition to the inner tube and the outer tube. The stent is restrictedly accommodated between the inner tube and the outer tube, with the outermost tube and the inner tube fixed outside the patient's body. Thereby stent does not move. In this construction, there may be friction between the outermost tube and the body cavity as well as the valve. But the outer tube is merely pulled to expand the stent. Therefore the stent hardly moves.
In the delivery system of the self-expandable stent proposed by the present applicant and described in JPA1996-252321, the stent little moves when the stent expands (discharged from system).
As the delivery system of the self-expandable stent, as described in the above-described WO96/31174 and JPA1996-252321, an “over the wire type” in which the guide wire lumen extends from the proximal end of a system to the distal end thereof. As the reason for the adoption of the “over the wire type”, the construction of discharging the stent from the appliance necessitates the outer sheath to be moved to the proximal side of the appliance.
When a plurality of stent delivery systems is prepared to implant the stent in the desired portion in the patient's body, systems having different outer diameters are used owing to a change of the outer diameter of the stent caused by the expansion thereof. Thus after a first stent delivery system is inserted into a blood vessel, it is exchanged with another system. In the “over the wire type”, the guide wire lumen is in penetration through the system from its distal end to its proximal end. To introduce the system into the patient's body, the guide wire is required to be not less than twice as long as the entire length of the system. Thus a long period of time is required to exchange the systems.
Recently the stent is demanded to be implanted in peripheral portions in the patient's body. Thus the development of a stent delivery system having a small diameter is strongly demanded.
The system of WO96/31174 is difficult to have a small diameter because it uses three tubular members.
Therefore it is a first object of the present invention to provide a stent delivery device, using a self-expandable stent, which facilitates an operation of exchanging the stent delivery device with a different stent delivery device in implanting a stent at a desired portion and has a small diameter.
As described above, the delivery system of the self-expandable stent has the construction in which the stent is restrictedly accommodated between an inner tube and an outer tube, and a locking portion for restricting the movement of the stent is provided in the inner tube at the position located at the proximal side of the stent. By pulling the outer tube toward the proximal side of a stent delivery device, the stent is released from the restricted state and expands itself. At this time, it is necessary for an operator to fix the inner tube to a certain position with one hand to prevent a stent-implanted position from moving forward and perform an operation of pulling the outer tube with the other hand. In implanting the stent in a bile duct through an endoscope, the inner tube cannot be fixed to a certain position. Therefore the operator performs an operation of adjusting the stent-implanting position by expanding the stent little by little and pulling the outer tube, with the operator holding the endoscope with one hand. To solve such a disadvantage in operability, a system having a housing assembly has been developed.
In US2004148009, the housing having the slider which can be moved in parallel is proposed. In this housing, the shaft is mounted inside the housing, and the proximal end of the outer tube is connected with the slider longitudinally movable inside the housing. The stent is released by sliding the slider toward the proximal side of the system. According to the description made in WO01/54614, the system can be operated with one hand. But actually in this system, it is necessary to use the housing by fixing it to a hard surface fixed to an operating table or a patient's leg. Thus the system has a low operability and has a possibility that the implanting position of medical appliances are set at an unintended position. In addition, this system necessitates the housing to be not less than twice as long as the entire length of the slider. Therefore the housing assembly is relatively large.
The housing assembly described in WO96/31174 has a construction similar to the above housing assembly and not less than two different operation modes different in the operation speed thereof. This system also necessitates the housing to be not less than twice as long as the entire length of the slider and thus the housing assembly to be relatively large. Therefore it is difficult to operate the system with one hand.
In the housing assembly disclosed in WO2002/087470, the proximal end of the outer tube is connected with the track inside the housing, and the track is gradually moved rearward by the ratchet means to thereby release the stent. The system can be operated with one hand. This system also necessitates the housing to be not less than twice as long as the entire length of the slider and thus the housing assembly to be relatively large.
Therefore it is a second object of the present invention to provide a stent delivery device, using a self-expandable stent, which facilitates an operation of exchanging the stent delivery device with a different stent delivery device in implanting a stent at a desired portion and does not move from an implanted position.